The present invention is related to disc drive data storage systems and, more particularly, to a method of controlling curvature of a hydrodynamic bearing slider.
Disc drives of the "Winchester" type are well known in the industry. Such drives use rigid discs coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor which causes the discs to spin and the surfaces of the discs to pass under respective head gimbal assemblies (HGAs). Head gimbal assemblies carry transducers which write information to and read information from the disc surface. An actuator mechanism moves the head gimbal assemblies from track to track across the surfaces of the discs under control of electronic circuitry. The actuator mechanism includes a track accessing arm and a load beam for each head gimbal assembly. The load beam provides a preload force which urges the head gimbal assembly toward the disc surface.
The head gimbal assembly includes a hydrodynamic (e.g. air) bearing slider and a gimbal. The gimbal is positioned between the slider and the load beam to provide a resilient connection that allows the slider to pitch and roll while following the topography of the disc. A slider includes a slider body having an air bearing surface which faces the disc surface. As the disc rotates, the disc drags air under the slider along the air bearing surface in a direction approximately parallel to the tangential velocity of the disc. Skin friction on the air bearing surface causes the air pressure between the disc and the air bearing surface to increase which creates a hydrodynamic lifting force that causes the slider to lift and fly above the disc surface. The preload force supplied by the load beam counteracts the hydrodynamic lifting force. The preload force and the hydrodynamic lifting force reach an equilibrium based upon the hydrodynamic properties of the slider and the speed of rotation of the disc. The transducer is typically mounted at or near the trailing edge of the slider.
Flying height is viewed as one of the most critical parameters of contact and non-contact recording. As the average flying height of the slider decreases, the transducer achieves greater resolution between the individual data bit locations on the disc. Therefore, it is desirable to have the transducers fly as close to the disc as possible. Flying height is preferably uniform regardless of variable flying conditions, such as tangential velocity variation from inside to outside tracks, lateral slider movement during seek operations and air bearing skew angles.
In certain applications, it is desirable to fabricate the slider such that the bearing surface has a positive curvature along the length and width of the slider. Length curvature is known as crown curvature. Width curvature is known as camber or cross curvature. The proper setting and control of length and width curvature improves flying height variability over varying conditions, improves wear on the slider and the disc surface, and improves takeoff performance by reducing stiction between the slider and the disc surface. In a typical slider fabrication process, length or width curvature is created by lapping the bearing surface on a cylindrically-shaped lapping surface or on a flat lapping surface while rocking the slider body back and forth in the direction of the desired curvature. The amount of curvature is determined by the radius of the rocking rotation. This lapping process is difficult to control and results in large manufacturing tolerances. More efficient and controllable methods of effecting air bearing surface curvature are desired.
U.S. Pat. No. 5,442,850 discloses inducing a preselected amount of compressive stress within a selected section of the bearing surface by impinging the section with a plurality of particles for a preselected amount of time. U.S. Pat. No. 4,910,621 discloses a method of producing curvature in a slider by creating a groove in the leading edge of the slider, placing a sealing material in the groove and then melting and stiffening the sealing material in the groove. The sealing material has an adhesive property upon melting and a shrinking property upon stiffening which causes lengthwise curvature at the leading edge of the slider. U.S. Pat. No. 5,220,471 discloses a slider having a longitudinal linear groove in a surface which is opposite the disc-opposing surface. The groove creates tensile stresses which cause the disc-opposing surface of the slider to be a curved surface in a convex form.